Preparation in a condition of purity of hydrocarbons from mixtures containing them



Jan. 3, 1950 s. F. BIRCH ETAL 2,493,557

PREPARATION IN A CONDITION OF PURITY OF HYDROCARBONS FRQM MIXTURES CONTAINING THEM Filed Feb. 1, 1946 BENZENE FREE PRODUCT FEED I V BE/YZENE H/GH BOILING J, I

HYDRO CARBONS: CYCLOHEXANE l ISOHEXANES n/vo LOWER/ BOILING MA TEE/A L Y i r CYCLOHEXANE AND BENZE/Vaf l v Y ISOHEPT/JNES AND HIGHER BOILING 2222252651 T/ON v MATERIAL THE INVENTORS Stanley Francis Birch John Habeshaw Clarence Barnes Collie /iZ A Mww Attorneyv Patented Jan. 3, 1950 PREPARATION: IN: A- CONDITION. OF PURITY F- HYDRQGARBONS FROM MIXTURES CONTAINING THEM Stanley Francis Birch, John Habeshaw, and Clarence Barnes Collis, S'unburyr-on-Thames, England, assignors to Anglo-Iranian Oil Company Limited, London, EngIand a British joint-stock corporation Application February 1, 1946;,S'e1'ialNo...64l4,96ll In Great Britain J anuary 12, 1 945 31 Claims. (Cl. 260-666) The-- invention relates to the. preparation of. hydrocarbons in a condition. of. purity from-hydro-- carbonmixtures containing them, and particular.- ly with the preparation of. pure cyclohexane and. benzene. in the utilisation of fractions consisting of orcontaining isomeric heptanes.

It. is among. the? objects of. the inventi'om to secure. the. desired. amounts of either cyclohexane: or benzene. or both. cyclohexane and; benzene. under conditions. and atsuch. a stage that the separation of pure products is simply and effec.-- tively carried out.-

In carrying out such operations animportant difficultyarises byreason, of the-presence of 2.4. dimethylpentaneand 2.2r-dimethylpentane in the fractions processed. We have now found that it. is possible. to convert these two parafiins into paraffins ot higher boiling point, that maybeseparatedfrom cycloheXa-neand benzene: by distillation. Thev natureof the conversions. maybe more readily understood; by reference to the. following table. in which the respective boiling. points of the. isomeric heptanesare set, out:

TABLE 1' Boiling. points, of the. isomeric heptames Boiling:

Hydrocarbon 2.2.3.-Trimethylbutane; 80. 88' 2. 2=Dimethy1pentane.- 78, 90. 2.4'-Dimethylpentane;- 80. 66* 3.3-Dimethylpentan 86:.10' z-Methylhexane 89. 67 2 3-D'imethylpentane 89.90- 3-Methylhexaue. 912 88 3-'Ethylpentane 93. 74 n-Heptane. 98: 2&

their separation from cyclo'hexane by anormalprocess of distillation. Itis by such a conversion that/ according-to the invention theseparati'o'n of recover the cyclohexane and/or benzene presentin the. feedstock in a pure. state,v and to hydrogenate. part. or all of they benzene present to. cyclohexane andcto. recover. the. cyclohexane soformed. Whenhowever benzene isthe product particularly required,. the object of the invention is: to de-- hydrogenate part. or all of. the cyclohexane and to. recovery the. benzene so formed in a pure state.

A further. objectof the invention is to convert the methylcyclopentane present to cyclohexane which may be recovered as such, or hydrogenated to yield benzene; and to convert the dimethylpentanes normally distilling with cyclohexane. to parafiins of different boiling, point, and. it required to. recover the parafiins so formed, thereby facilitating the recovery of pure benzene and pure cyclohexane.w

Thus according: to the invention a considerable amount of. benzene and cyclohexane may be recovered pure, from feedstocks not. formerly easily treated to yield these compounds in a pure state.

According to the invention a hydrocarbon fraction consisting essentially of n-hexane, benzene; methylcyclopentane, cyclohexane, and dimethylpentanes. is distilled, with. or without the addition under known conditions of an azetrope. forming hydrocarbon, so that substantially pure cyclohexane is recovered as residual fraction, the

overhead fraction comprising any cyclohexane.

not so removed, and all the other constituents of the" fraction distilled being treated by' a process of extractive distillation; or azetropic distillation or solvent extraction, whereby substantially the whole of the benzene present is. recovered, the benzene-freed fraction being then passed to an isomerisation zone, where a substantial party of the methylcyclopentane content is converted to cyclohexane' and a substantial part of. the 2.2 dimethylpentane and 2.4'-dimethylpentane to iso-heptanes of different boiling point, the product' of this isomerisation being thenv fractionally distilled and a fraction, consisting of cyclohexanel unchanged methylcyclopentane, n-hexane and covered separately or in the benzene recovery stage of the process.

The conversion of the 2.2- and 2.4-dimethylpentanes to higher boiling heptane's is not accompanied by any significant formation of lower boiling hydrocarbons such as butanes. The following example illustrates th e operation of the, isomerisation:

A cyclohexane cut from Iranian isoheptane was extractively distilled using aniline as solvent, and from this extractive distillation a fraction of the following composition obtained- (weigh percent.)

i Per cent Methylcyclopentane 'cyclohexane' (equilibrium mixture at 80 c., see Table 2) 45.6 Paramns, 2.2.- and 2.4-dimethylpentane 54.4

The benzene was almost completely removed during the extractive distillation; being present in the above fraction to an extent less than 0.5 percent. This product isomerisation.

520 g. of this feedstock was stirred for 2 hours with 150 g. of aluminium chloride at 79 0., a slow stream of hydrogen chloride being passed through the reaction mixture. At the end of this time the reaction product was separated, soda and water washed and dried and fractionated in a 50-p1ate batch column.' 13 per cent. by weight of the total product consisted of heptane paraffins boiling between 84 C.

and 91 C., the remainder being distillate comprising methylcyclopentane and Cyclohexane in proportions agreeing with the equilibrium compositions at the reaction temperature (79 C.) indicated in Table 2 and unchanged 2.2- and 2.4-dimethylpentanes. From these results 25 per cent. of the original 2.2- and 2.4-dimethylpentanes was converted to higher boiling heptanes and no significant formation of lower hydrocarbons such as butanes was detected.

The foregoing example illustrates the conversion of the 2.2- and 2.4-dimethylpentanes to higher boiling heptanes. The main heptanes formed were 2.3- and 3.3-dimethylpentanes, some methylhexanes but no ethylpentane being also detected.

The. invention is hereinafter described with reference to the accompanying diagrammatic drawing.

In carrying the invention into effect as illustrated-in the accompanying drawing any hydrocarbon fraction containing the compounds n-hexane, methylcyclopentane, cyclohexane, benzene and dimethylpentanes may serve as feedstock 'to the process. The presence of higher boiling constituents that is, above 81.1 C. is

not important, since these may be removed in the initial fractionating zone a. It is however advantageous to remove lighter boiling hydrocarbons from the feedstocks ifpresent in any large amount before subjection to the process of the invention. A suitable feedstock to the process is for exserved as feedstock to the p ample an isoheptane fraction from Iranian naphtha, which was fed to the fractionation zone a and gave an overhead fraction comprising 51 per cent. by weight of the total material. The

5 overhead fraction had a boiling range of 68 C.-

81.1 C. and the following composition (weight per cent) n-Hexane 7.5

Methylcyclopentane 25.0

Benzene 10.6

Cyclohexane 46.1 C7 Parafiins (2.2-dimethylpentane and 2.4-dimethylpentane) 10.8

The overhead fraction was then passed to the second fractionation zone b, where by distillation in the presence of an azeotrope forming hydrocarbon, which may or may not be added to the fraction, a residual fraction was prepared 29 comprising substantially pure cy-clohexane, the remaining constituents of the charge together with any cyclohexane not removed in the residual fraction comprising the overhead fraction. The amount of Cyclohexane taken off in this overhead fraction from the fra ctionating zone I) depends on the efiiciency of fractionation and on the composition of the charge passed to the second fractionating zone I). V

The overhead fraction from the fractionation zone b passes to a zone 8 where by extractive distillation, azeotropic distillation, or solvent extraction, the benzene is recovered practically pure. The operation of an extractive distillation g proces's of this character for the separation of aromatic hydrocarbons is described in the specification of the United States Patent No. 2,288,126.

The application of azeotropic distillation is discussed in Research Paper RP. 1402 of the U. S. O National Bureau of Standards. The use of solvent extraction in the zone s is also within the scope of the invention, either alone or when extractive distillation or azeotropic distillation is also employed. Benzene recovered in the zone s may be used as the added hydrocarbon azeotrope forming component in the distillation if such addition be required and the required amount may be passed from the zone s to the feed to the fractionating zone 22.

The benzene-freed product from the zone 8 passes to the catalytic isomerisation zone 2'. Here it is subjected to catalytic conversion whereby a substantial proportion of the methylcyclo- .pentane is converted to cyclohexane, and a substantial proportion of the 2.4-dimethylpentane and 2.2-dimethylpentane, to hydrocarbons of different boiling point, and especially to isoheptanes of higher'boiling point. The catalyst used in the catalytic isomerisation zone 2 is preferably of the 60 Friedel-Crafts type, aluminum chloride and catalysfs prepared from or containing aluminum chloride being especially suitable. tions of hydrogen halides may be added as catalyst activators as is usual in conversions of the 5 type using Friedel-Crafts catalysts, particularly halides of aluminum. Although such Friedel- Crafts catalysts are preferred, the use of other catalysts in the isomerisation zone is within the scope of the invention, and may in fact be advan- 7 tageous when the benzene separated in the zone 8 is hydrogenated. Some hydrogenation catalysts are known to have activity in conversions such as those indicated. The oxides and sulphides of metals as catalysts in the zone s may therefore be used.

Minor proporamass? There are a number of known conditions in which isomerisation :may be carried Out in the catalytic isomerisation stage i .of the process. Thus the benzene-freed product from the zone 5 may be fractionated into two fractions, the lower boiling fraction containing the bulk of the methylcyclopentane, and the higher boiling fraction substantially the whole of the cyclohexane and dimethylpentanes. The lower boiling fraction contains normal hexane and methylcyciopentane, and possibly minor proportions of isohexanes. The two fractions may be isomerised separately. The isomerisation of the lower boiling fraction is readily carried out with substantial conversion of the methylcyclopentane to cyclohexane, and partial conversion of the normal hexane to isohexane. The isomerisation product of this fraction may be passed to the distillation zone a, or to the fractionating zone 1) after removal by sepa rate fractionation of the higher boiling products of side reactions. The higher boiling fraction from the fractionating zone s, containing some methylcyclopentane, cyclohexane, 2.4-dimethylpentane and 2.2-dimethylpentane is passed to a separate isomerisation zone, operated under conditions whereby a substantial proportion of the 2.4- and 2.2-dimethylpentanes are converted to hydrocarbons of different boiling point, especially to higher boiling iso-heptanes. In order to avoid isomerisation of the cyclohexane to methylcyclopentane in the zone 2', it is advantageous that this higher boiling fraction be so prepared that the methylcyclopentane and cyclohexane are present in the proportions corresponding to the equilibrium mixture of these isomers at the temperature of isomerisation. These equilibrium compositions are indicated in the following Table 2:

TABLE 2 Equilibrium concentrations of methylcyclopentane and cyclohexane Mole per cent Temperature, Mole per cent,

C. gg gggg Cyclohexane (Glasebrook and Lovell, J. Amer. Chem. Soc., 61, 1717 (1939), Sclzmit, Hoog, and Verhuos, Roe. Trav. 0111111., 59, 793-810 (1940)) The isomerisation product of this higher boiling fraction may then be passed to the fractionation zone a, where high boiling constituents are removed. Suflicient additional benzene from the zone s should be passed with the feed to the fractionation-zone b to ensure the removal of the 3 z, and there subjected to catalytic conversion in one or more stages, as hereinbefore described. The product from this conversion is then passed to the fractionating Zone 0, where the higher boiling paraifins, especially branched-chain hept-anes are recovered, and any lighter boiling conversion products (principally isohexanes) are removed, the remainder .of the product, comprising unchanged n-hexane, dimethylpentanes, methylcyclopentane and cyclohexane being then passed to the fractionation zone b.

In the operation of the fractionation stage in zone 1), and its co-relation with conditions .of operation in other stages of the process, it is important that the amount of benzene fed from the zones to the fractionation :zone b be adjusted to allow for the amount of paraffins recycled to the fractionation zone b from the isomerisation zone 2 as hereinbefore described. It is also im-' portant, whether the benzene-freed product be passed in two fractions or as a whole, that all processing conditions comprising catalyst volume, contact time and temperature be regulated so that the amount of 2.4- and 2.2-dimethylpentane converted to hydrocarbons of different boiling point, be at least equivalent to the amount of those parafiins introduced into the system in the feed to the fractionation zone :1, otherwise the amount of those paraihns in the system will increase and ultimately may interfere with the operation in other stages of the process, particularly with that of the fractionation zone I).

If it be required to produce a large yield of benzene, the product from the isomerisation zone i may be passed to the dehydrogenation zone (1, whereby in the catalytic dehydrogenation, the cyclohexane present may be converted to benzene, which may be recovered the zone 3 or separately.

A preferred method of operating in the manner immediately before described is to pass to the dehydrogenating zone d the product of isomerisation of higher boiling fraction of the benzene-free product from the zone .9, after removal of the higher boiling heptanes as hereinbefore described, the benzene being recovered separately from the products of dehydrogenation. Obviously also cyclohexane formed in preceding zones, as in the fractionation zone 5 may advantageously be dehydrogenated to benzene in known manner in the zone d, if the main product required is benzene.

Processes of dehydrogenation for the production of benzene from cyclohexane and the course of reaction with parafiins are described in the following prior literature, viz: British Patent No. 563,555, United States Patent No. 2,357,694, German Patent No. 516,251, German Patent No.

626,273, German Patent No. 629,838, by Maihle,

Marty and Gaudry, Comp. Rend. 194, 1947 (1932), and by Taylor and Jones, Bull. Soc. Chim. Belg. 46, 241-252. (1937).

The dehydrogenation may be efiected with oxides or sulphides of metals as isomerisation catalysts, either alone or on porous supports, approximately in the temperature range ZOO-600 C.

The ease with which the benzene formed by dehydrogenation may be separated from the paraffins present as compared with the relative difficulty of separating these paraffins from cyclohexane is one of the advantages following from the operation of the dehydrogenation stage in the manner indicated. Alternatively, if the production of cyclohexane is the main object intended, part or whole of the benzene recovered 1 in' the zone s may be hydrogenated to yclo-' hexane in the hydrogenation zone It. A disadvantage of such hydrogenation'under known conditions'is that the last traces of benzene are difiicult to remove from the treated stock and thus the cyclohexane produced is impure. In the process of the invention sufiicient benzene is left unhydrogenated in the zone h, either by by-passing part of the benzene from the zone s past the zone 71, or by regulation of the conditions in the zone h to ensure that when the total material from the zone It is passed with the isomerisation product from the zone to' the fractionation zone a or b, sufficient benzene is present in the totalv feed to the fractionation zone b to ensure that all the dimethylpentanes are removed overhead and substantially pure cyclohexane left as the residual fraction. Thus the cyclohexane present in the feed, that produced in the isomerisation' zone 1 and that produced by the hydrogenation of the benzene, are all recovered in the fractionation zone b. In this way the benzene may be used in the separation of the cyclohexane and later converted to cyclohexane, it being understood that the presence of unchanged benzene in the hydrogenation product has no effect on the substantial purity of the cyclohexane product.

7 It will be understood that the invention is not confined to the sequence of operations hereinbefore described by way of example.

We claim:

1. A process for the preparation of a pure hydrocarbon from a feedstock consisting essentially of n-hexane, benzene, methylcyclopentane, cyclohexane and 2,2and 2,4-dimethylpentanes, which comprises the distillation of the feedstock in an initial distillation zone to remove a primary fraction distilling at a temperature not above 811 0., the primary fraction being distilled ina second distillation zone in the presence of sufficient azeotrope-forming hydrocarbon, such as benzene, to ensure the recovery of pure cyclohexane as a, residual fraction, an overhead fraction also being taken, comprising any cyclohexane not retained in the residue fraction, together with azeotropic mixtures comprising methylcyclopentane and dimethylpentanes with benzene and any other azeotrope-forming hydrocarbon present, together with all other constituents of the feedstock to the second distillation zone, the overhead fraction then being subjected to extractive distillation whereby substantially the whole of the benzene in the overhead fraction is recovered in association with the extraction medium and a benzene-freed fraction produced, the said benzene-freed fraction being then passed to an isomerization zone in which a substantial part of its methylcyclopentane content is converted into cyclohexane, and a substantial part of the 2,2-dimethylpentane and 2,4-dimethylpentane converted to hydrocarbons of difierent boiling point.

2. A process for the preparation of a pure hydrocarbon as specified in claim 1 in which benzene is separated from the extraction medium, as by distillation and is recycled to the second distillation zone.

3. A process for the preparation of a pure hydrocarbon, as specified in claim 1 in which benzene is separated from the extraction medium as by distillation and hydrogenated and the cyclohexane so formed recycled to the second-distillation zone.

4. A process for the preparation of a pure hydrocarbon as specified in claim 1, in which the product of isomerization is subjected to distillation and a fraction containing cyclohexane, unchanged methylcyclopentane, normal hexane and iso-heptane is recycled to the second distillation zone.

5. A process for the preparation of a pure hydrocarbon as specified in claim 1 in which the product of isomerization is subjected to distillation to take overhead a fraction containing methylcyclopentane and hexanes, a middle fraction containing n-hexane, dimethylpentanes, methylcyclopentane and cyclohexane being recovered and recycled tothe second distillation zone and higher boiling paraffins recovered as a bottoms product.

6. A process for the preparation of a pure hydrocarbon as specified in claim 1, in which at least a part of the isomerization product is dehydrogenated to benzene and the benzene recycled to the second distillation zone.

7. A process for the preparation of a pure hydrocarbon as specified in claim 1, in which the fraction obtained in the initial fractional distillation and subjected to distillation in the second distillation zone has a boiling range of 69-81 C. and. contains the whole of the methylcyclopentane, cyclohexane and benzene present in the feedstock.

8. A process for the preparation of a pure hydrocarbon as specified in claim 1, in which the benzene-freed product from the extractive distillation zone is fractionally distilled to separate a methylcyclopentane-enriched fraction from an iso-heptane-enriched fraction, the methylcyclopentane-enriched fraction passed to an isomerisation zone in which a substantial amount of its methylcyclopentane content is converted to cyclohexane and at least part of the isomerisation product passed to the second distillation zone.

9. A process for the preparation of a pure hydrocarbon as specified in claim 1, in which an azeotrope-forming hydrocarbon is added to the feedstock to the second distillation zone.

10. A process for the preparation of a pure hydrocarbon as specified in claim 1 in which benzene is added to the feedstock to the second distillation zone. v

11. A process for the preparation of a pure hydrocarbon from a feedstock consistin essentially of n-hexane, benzene, methylcyclopentane, cyclohexane and 2,2- and 2,4-dimethylpentanes, which comprises the distillation of the feedstock in an initial distillation zone to remove a primary fraction distilling at a temperature not above 81.1 C., the primary fraction being distilled in a second distillation zone in the presence of sufficient azeotrope forming hydrocarbon, such as benzene, to ensure therecovery of pure cyclohexane as a residual fraction, an overhead fraction also being taken, comprising any cyclohexane not retained in the residue fraction, together with azeotropic mixtures comprising methylcyclopentane and dimethylpentanes with benzene and any other azeotrope-forming hydrocarbon present, together with all other constituents of the feedstock to the second distillation zone, the overhead fraction then being subjected to solvent extraction whereby substantially the whole of the benzene in the overhead fraction is recovered in association with the solvent extraction medium and a benzene-freed fraction produced, the said benzene-freed fraction being then passed to an isomerisation zone in which a substantial part of its methylcyclopentane content is converted into :cyclohexane, and a substantial part boiling point.

12. A process for the preparation of a pure hydrocarbon as specified in claim 11 iii-which benzene :is separated from :the solvent extraction medium, as by distillation and is recycled to :the second distillation zone.

13. A process .for the preparation of a pure hydrocarbon as specified in claim .11 in which banzene is separated from the extraction medium as by distillation and hydrogenated and the cyclohexane so formed recycled to the second distillation zone.

14. A process for the preparation .of a pure hydrocarbon .as specified in claim 11 in. which the product of isomerisation is subjected to distillation and a fraction containing cyclohexane, unchanged methylcyclopenia-ne,normal hexane and iso-heptane is recycled to the second distillation zone.

15. A process -for the preparation of a pure hydrocarbon as specified in claim 11 in which the product of isomerisation is subjected to distillation to take overhead a fraction containing methylcyclopentane and hexanes, a middle fraction containing n-hexane, dimethylpentanes, methylcyclopentane and cyclohexane being recovered and recycled to the second distillation zone and higher boiling paraihns recovered as a bottoms product.

16. A process for the preparation of a pure hydrocarbon as specified in claim 11 in which at least part of the isomerisation product is dehydrogenated to benzene and the benzene recycled to the second distillation zone.

17. A process for the preparation of a pure hydrocarbon as specified in claim 11, in which the fraction obtained in the initial fractional distillation and subjected to distillation in a second distillation zone has a boiling range of 69-81 C. and contains the whole of the methylcyclopentane, cyclohexane and benzene present in the feedstock.

18. A process for the preparation of a pure hydrocarbon as specified in claim 11 in which the benzene-freed product from the solvent extraction zone is fractionally distilled to separate a methylcyclopentane-enriched fraction from an isoheptane-enriched fraction, the methylcyclopentane-enriched fraction passed to an isomerisation zone in which a substantial amount of its niethylcyclopentane content is converted to cyclohexane and at least part of the isomerisation product passed to the second distillation zone.

19. A process for the preparation of a pure hydrocarbon as specified in claim 11 in which an azeotrope-forming hydrocarbon is added to the feedstock to the second distillation zone.

20. A process for the preparation of a pure hydrocarbon as specified in claim 11 in which benzene is added to the feedstock to the second distillation zone.

21. A process for the preparation of pure hydrocarbon from a feed stock consisting essentially of n-hexane, benzene, methylcyclopentane, cyclohexane and 2,2- and 2,4-dirnethylpentanes, which comprises the distillation of the feedstock in an initial distillation zone to remove a primary fraction distilling at a temperature not above 81.1 (3., the primary fraction being distilled in a second distillation zone in the presence of sufficient azeotrope forming hydrocarbons, such as ilO :benzene, 'to ensure "the recovery .of pure cyclohexane as a residual -:fractlon, .an .overhead fraction also being taken, .acomprising any .cyclohexane not retained in the residue fraction, together with .azeotropic mixtures comprising methylcyclopentane and :dimethylpentanes with ibenzene and any other azeotropeforming hydrocar- 'bon present, :together with all other constituents :of :the- Eieedstockto the second distillation zone,

:the overhead fraction then 'being subjected :to

.azeotropic distillation whereby substantially the wholeof the i benzene in the overhead fraction is recovered-and a benzene-freed fraction produced,

the said benzene-freed fraction be'ing then passed to an isomerisation zone in 'Which a substantial part of its 'methylcyclopentane :content :is converted :into cyclohexane, and a substantial part of the 2.2-dimethylpentane and :2-,=4-dimethylpentane converted to' hydrocarbons o'f :difierent :is recycled to the second distillation zone.

'23. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which benzene recovered in the azeotropic distillation is hydrogenated and the cyclohexane so formed recycled to the second distillation zone.

24. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which the product of isomerisation is subjected to distillation and a fraction containing cyclohexane, unchanged methylcyclopentane, normal hexane and isoheptane is recycled to the second distillation zone.

25. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which the product of isomerisation is subjected to distillation to take overhead a fraction containing methylcyclopentane and hexanes, a middle fraction containing n-hexane, dimethylpentanes, methylcyclopentane and cyclohexane being recovered and recycled to the second distillation zone and higher boiling parafiins recovered as a bottoms product.

26. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which at least part of the isomerisation product is dehydrogenated to benzene and the benzene recycled to the second distillation zone.

2'7. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which the fraction obtained in the initial fractional distillation and subjected to distillation in a second distillation zone has a boiling range of (SQ-81 C. and contains the whole of the methylcyclopentane, cyclohexane and benzene present in the feedstock.

28. A process for the preparation of a pure hydrocarbon as specified in claim 21 in which the benzene-freed product from the azeotropic distillation zone is fractionally distilled to separate a methylcyclopentane-enriched fraction from an isoheptane-enriched fraction, the methylcyclopentane-enriched fraction passed to an isomerisation zone in which a substantial amount of its methylcyclopentane content is converted to cycloheXane and at least part of the isomerisation product passed to the second distillation zone.

29. A process for the preparation of a pure hydrocarbon as specified in claim 21in which an azeotrope-forming hydrocarbon is added to the feedstock to the second distillation zone.

":11 :30. A'pro'cess for the'preparation of a pure hydrocarbon as specified "in claim 21 in .which benzene is added to the feedstock to the second distillation zone.

31. A process for the preparation of a pure hydrocarbon from a feedstock consisting essentially of n-hexane, benzene, methylcyclopentane,

-hexane as a residual fraction, an overhead fraction also being taken, comprising any cyclohexam not retained in the residue fraction, together With. azeotropic mixtures comprising methylcyclopentane and dimethylpentanes with benzene and any other azeotrope-forming hydrocarbon present, together with all other constituents of the feedstock to the second distillation zone, the overhead fraction then being treated for the recovery .of substantially the whole of the benzene in the overhead fraction and the productionof a benzene-freed fraction, the said benzene-freed fraction being then passed to an isomerisation zone in which a substantial part of its methylcyclopentane content is converted into cyclohexane, and a substantial part of the 2,2-dimethylpentane and 2,4-dimethylpentane converted to hydrocarbons of difierent boiling point.

STANLEY FRANCIS BIRCH.

JOHN HABESHAW.

CLARENCE BARNES COLLIS,

REFERENCES CITED 1 The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,212,810 Field Aug. 27, 1940 2,288,866 Hoog July 7, 1942 2,299,716 Van Peski Oct. 20, 1942 2,356,240 Hamlin Aug. 22, 1944 2,382,446 Ross et a1. Aug. 14, 1945 2,440,414

Oblad Apr. 27, 1948 

31. A PROCESS FOR THE PREPARATION OF A PURE HYDROCARBON FROM A FEEDSTOCK CONSISTING ESSENTIALLY OF N-HEXANE, BENZENE, METHYLCYCLOPENTANE, CYCLOHEXANE AND 2,2- AND 2,4-DIMETHYLPENTANES, WHICH COMPRISES THE DISTILLATION OF THE FEEDSTOCK IN AN INITIAL DISTILLATION ZONE TO REMOVE A PRIMARY FRACTION DISTILLING AT A TEMPERATURE NOT ABOVE 81.1*C., THE PRIMARY FRACTION BEING DISTILLED IN A SECOND DISTILLATION ZONE IN THE PRESENCE OF SUFFICIENT AZEOTROPE-FORMING HYDROCARBON, SUCH AS BENZENE, TO ENSURE THE RECOVERY OF PURE CYCLOHEXANE AS A RESIDUAL FRACTION, AN OVERHEAD FRACTION ALSO BEING TAKEN COMPRISING ANY CYCLOHEXANE NOT RETAINED IN THE RESIDUE FRACTION, TOGETHER WITH AZEOTROPIC MIXTURES COMPRISING METHYLCYCLOPENTANE AND DIMETHYLPENTANES WITH BENZENE AND ANY OTHER AZEOTROPE-FORMING HYDROCARBON PRESENT, TOGETHER WITH ALL OTHER CONSTITUENTS OF THE FEEDSTOCK TO THE SECOND DISTILLATION ZONE, THE OVERHEAD FRACTION THEN BEING TREATED FOR THE RECOVERY OF SUBSTANTIALLY THE WHOLE OF THE BENZENE IN THE OVERHEAD FRACTION AND THE PRODUCTION OF A BENZENE-FREED FRACTION, THE SAID BENZENE-FREED FRACTION BEING THEN PASSED TO AN ISOMERISATION ZONE IN WHICH A SUBSTANTIAL PART OF ITS METHYLCYCLOPENTANE CONTENT IS COVERTED INTO CYCLOHEXANE, AND A SUBSTANTIAL PART OF THE 2,2-DIMETHYLPENTANE AND 2,4-DIMETHYLPENTANE CONVERTED TO HYDROCARBONS OF DIFFERENT BOILING POINT. 